Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 104,388	$ 121,021	$ 112,566
Securities available for sale:
Unrealized net holding gains (losses) arising during the period, gross	23,204	25,836	(11,985)
Tax effect	(5,800)	(6,459)	2,996
Unrealized net holding gains (losses) arising during the period, net	17,404	19,377	(8,989)
Reclassification adjustment for net (gains) losses in net income, gross	(3)	79	6,622
Tax effect	1	(20)	(1,655)
Reclassification adjustment for net (gains) losses in net income, net	(2)	59	4,967
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, gross	644	737	688
Tax effect	(161)	(184)	(172)
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, net	483	553	516
Total securities available for sale, net	17,885	19,989	(3,506)
Cash flow hedges:
Unrealized (losses) gains on derivatives (cash flow hedges), gross	(275)	(459)	1,218
Tax effect	69	115	(304)
Unrealized (losses) gains on derivatives (cash flow hedges), net	(206)	(344)	914
Reclassification of net unrealized losses (gains) on cash flow hedges to interest (income), gross	296	(2,012)	(2,300)
Tax effect	(74)	503	575
Reclassification of net unrealized losses (gains) on cash flow hedges to interest (income), net	222	(1,509)	(1,725)
Total cash flow hedges, net	16	(1,853)	(811)
Pension and other benefits:
Amortization of prior service cost and actuarial losses, gross	1,627	2,686	1,145
Tax effect	(407)	(672)	(286)
Amortization of prior service cost and actuarial losses, net	1,220	2,014	859
Decrease (increase) in unrecognized actuarial loss, gross	429	5,331	(12,457)
Tax effect	(107)	(1,333)	3,038
Decrease (increase) in unrecognized actuarial loss, net	322	3,998	(9,419)
Total pension and other benefits, net	1,542	6,012	(8,560)
Total other comprehensive income (loss)	19,443	24,148	(12,877)
Comprehensive income	$ 123,831	$ 145,169	$ 99,689